Jules and Jim (1962) is really the story of Catherine, a woman so strong-willed that even Francois Truffaut can't let her be the center of her own story. The last line -- "But it was not allowed." -- sums up his view, or at least society's.
The problem is that the love triangle at the center of the story is based on reality, and while the three of them did eventually part ways none of them committed murder or suicide. Society may have made the relationship untenable in reality, but it did not push anyone to murderous psychopathy. Perhaps Truffaut himself knew that presenting this relationship as actually working is what is truly not allowed, but it seems like that's not even a thing he wanted to do. Oops.